Typical automotive engine cooling fan assemblies include an axial flow fan coupled to the rotating portion of an electric motor. The fan includes a hub and a plurality of fan blades. The hub is connected to the rotating portion of the motor with screws, clips, or other fastening methods. Additionally, the hub may be press-fit onto the rotating portion of the motor. The fan blades radially extend away from the hub. Rotation of the fan by the electric motor causes the fan to generate an airflow, which is generally parallel to an axis of rotation of the fan. The airflow is used to remove heat from the automobile's powertrain and/or the air conditioning condenser of the automobile.
When the electric motor rotates the fan, the fan exhibits at least some level of noise and vibration originating from the electric motor. The noise is caused by numerous factors including the type of electric motor and the design of the fan. In at least some instances, noise is caused by, for example, motor electromagnetic forces exciting resonances of the motor and/or the fan. The noise emitted by the fan due to the electric motor typically does not impact the magnitude of airflow generated by the fan; however, users of the fan typically find levels of noise above a certain threshold to be bothersome.
It would therefore be desirable for an axial flow fan to generate an airflow without generating bothersome levels of noise due to the electric motor.